This is the first Resubmission of a Renewal application of a funded AREA award (R15) that has allowed the Principal Investigator to initiate a new research program related to aging and neurodegenerative diseases. As by-products of cellular respiration, a variety of reactive oxygen species (ROS) are formed that can be highly damaging to most types of cellular macromolecules. Several degenerative disorders commonly associated with aging, including Alzheimer's, Parkinson's Disease and Amyotrophic Lateral Sclerosis (ALS), are thought to involve oxidative damage. Methionine, an amino acid commonly found in protein, is readily oxidized to form methionine sulfoxide, which often compromises enzyme activity. Methionine sulfoxide reductases (Msr) are a ubiquitous class of enzymes that specifically repair oxidized methionine residues in proteins. Drosophila has two known genes, MsrA and MsrB, that encode proteins with Msr activities. The Progress Report describes isolation and characterization of MsrA- MsrB- genetic mutants of Drosophila that are deficient for any known Msr activity. Preliminary results show that these animals have heightened sensitivity to oxidative stress and they may have a motor and/or neurological defect since mobility, especially climbing, is severely impaired. A major question in the field is whether the mitochondria are the major site of action for Msr proteins since mitochondria are the primary source of intracellular reactive oxygen species (ROS). Proposed experiments include expression of MsrA+ and MsrB+ transgenes encoding Msr proteins with signal sequences to direct the polypeptides to either the mitochondria or cytoplasm in the Msr-deficient Drosophila strains. These experiments will allow direct testing of the hypothesis that Msr activity is most critical in the mitochondria. Numerous studies have implicated neurons as an especially sensitive target for oxidative damage. Proposed experiments also include investigation of the effect of Msr deficiencies on the production of dopamine and the physiology of dopaminergic neurons. Degeneration of the dopaminergic neurons and loss of dopamine is central to Parkinson's Disease. These experiments should lend insight into the possible involvement of oxidative stress on aging and the development of Parkinson's Disease as well as other age- related neurodegenerative diseases such Alzheimer's and Amyotrophic Lateral Sclerosis (ALS). [unreadable] PUBLIC HEALTH RELEVANCE: Oxidative damage is widely considered to be a major factor in the aging process and the development of neurodegenerative diseases such as Alzheimer's, Parkinson's Disease and Amyotrophic Lateral Sclerosis (ALS). Methionine sulfoxide reductases are a ubiquitous class of enzymes that repair oxidative damage to methionine in proteins. This project uses Drosophila (fruit flies) as a genetic model to investigate effects on aging and neurological function when this critically important damage-repair pathway is compromised. [unreadable] [unreadable]